A variety of medical treatments and surgical methods entail implanting an elongated structure in the body of a human or veterinary patient. Examples of such elongated structures include catheters, sheaths and cardiac electrical leads (such as pacemaker leads and defibrillator leads), and a variety of other devices. Over time, it may become necessary or desirable to remove such an elongated structure from the body of the patient. However, problems may be encountered in attempting removal of an elongated structure implanted in biological tissue.
For example, a heart pacemaker is typically implanted in a subcutaneous tissue pocket in the chest wall of a patient, and a pacemaker lead positioned in the vascular system of the patient, extending from the pacemaker and through a vein into a chamber of the patient's heart. The pacemaker lead commonly includes a coiled structure such as an electrical wire coil for conducting electrical signals (such as stimulating and/or sensing signals) between the pacemaker and the heart. Defibrillator leads are generally similar and, like pacemaker leads, are located about the heart, but are affixed both internally and externally of the heart. A typical lead includes one or more coaxial or lateral helical wire coils having a hollow inner passageway that extends the entire length of the wire coil or coils. The wire coils are surrounded by an electrically insulating material such as a flexible tube, sheath or coating. The insulating material may be silicone or polyurethane, and serve simultaneously to protect the wire coils from body fluids and to insulate the wire coils from one another.
While cardiac electrical leads typically have a useful life of many years, over time pacemaker and defibrillator leads unfortunately become encapsulated by fibrotic tissue against the heart itself or the wall of the vein, or against other surrounding tissue. Encapsulation is especially encountered in areas where the velocity of the flow of blood is low. The fibrotic tissue is tough and makes it difficult to remove the lead from the area of the heart without bleeding or other trauma to the area. For example, when small diameter veins through which a pacemaker lead passes become occluded with fibrotic tissue, separating the lead from the vein can cause severe damage to the vein or even destruction of it. Furthermore, separation of the lead from the vein is usually not possible without restricting or containing movement of the lead, that is, fixing the lead in position with respect to the patient, in particular, with respect to the patient's vein.
To avoid this and other possible complications, some useless pacemaker or other leads are simply left in the patient when the pacemaker or defibrillator is removed or replaced. However, such a practice can incur the risk of an undetected lead thrombosis, which can result in stroke, heart attack, or pulmonary embolism. Such a practice can also impair heart function, as plural leads can restrict the heart valves through which they pass.
There are of course many other reasons why removal of a useless lead is desirable. For example, if there are too many leads positioned in a vein, the vein can be obliterated. Multiple leads may be incompatible with one another, interfering with their pacemaking or defibrillating function. Of course, an inoperative lead can migrate during introduction of an adjacent second lead, and mechanically induce ventricular arrhythmia. Other potentially life-threatening complications can require the removal of the lead as well. For example, removal of an infected pacemaker lead is desirable, so as to avoid septicemia or endocarditis. Surgical removal of a heart lead in such circumstances often involves open heart surgery, with its accompanying risks, complications and significant costs.
A variety of successful methods and apparatus have been devised as alternatives to open heart surgery for heart lead removal. For example, U.S. Pat. No. 5,697,936 (Shipko et al., Dec. 16, 1997) discloses a device for removing from a patient a previously implanted elongated structure such as a catheter, a sheath, a defibrillator lead, a pacemaker lead or the like. The device disclosed by Shipko et al. includes a snare having one or more proximal or distal loops which can encircle and reversibly grasp either the proximal end or the distal end of the elongated structure to be removed. The device also includes a sheath member for delivering the snare loop or loops to the particular end of the elongated structure which is to be grasped. In some disclosed embodiments for grasping the distal end of the elongated structure, the sheath member is advanced along the elongated structure and separates the structure from any tissue which has encapsulated the structure after its implantation. The snare can be either positioned over or contained within a second sheath located in the sheath member. The patent does not appear to disclose any way for the snare loop or loops to be extended beyond the distal end of the sheath member, however.
Numerous other devices for snaring fragments or foreign bodies have been disclosed. For example, U.S. Pat. No. 5,171,233 (Amplatz et al., Dec. 15, 1992) is directed to a snare-type probe in which kinking of a snare loop is obviated by the use of a shape memory material for the snare. More particularly, the snare is composed of nitinol (nickel-titanium alloy system) wire in a superelastic state, having a transition temperature below the operating temperature of the snare, for example, below body or room temperature. This allows the snare to be manipulated in a relatively severe manner during introduction into a patient, but to recover its desired shape after such manipulation, without kinking or other deformation. The loop of the snare of the device is oriented at an angle with respect to an elongate proximal member on which it is carried.
U.S. Pat. No. 5,562,678 (Booker, Oct. 8, 1996) discloses a reversible snare for grasping and retrieving an article such as a cardiac lead, which includes a retractable closed loop carried by a sheath member adapted for introduction into a patient. The closed loop of the snare is composed of nitinol or another shape memory material and defines a hook adapted to partly encircle the cardiac lead. The snare also includes a threader also carried by the sheath member; the threader is reversibly extendable through the closed loop, like a thread through a needle's eye, so that the hook and threader together fully encircle the lead. Retraction of the closed loop causes the hook and threader to close around the lead and permit its withdrawal into the sheath member. There appears to be no disclosure of any way in which the cardiac lead could be received through only the closed loop of the snare itself.
Finally, U.S. Pat. No. 5,318,527 (Hyde et al., Jun. 7, 1994) is directed to a system for removing an in-place intravascular device (such as a catheter or guidewire) from a patient's body lumen, such as from a coronary artery, in which a catheter or other similar device is advanced through the vascular system alongside the in-place device until its distal end is located at a desired location within the vascular system. The disclosed removal system includes an exchange catheter having a flexible strand which forms a loop at the distal end of the catheter, the loop being adapted to be disposed about the catheter or guidewire that is in-place within the patient. The exchange catheter includes a lumen through which the strand passes and from which the loop extends. The exchange catheter does not appear to be dimensioned or otherwise adapted for receiving the in-place catheter or guidewire within the exchange catheter as the exchange catheter is advanced. To the contrary, it is an express purpose of the disclosed device to maintain access to a region of the body lumen about the distal end of the in-place catheter or guidewire during use of the exchange catheter, and receipt of the in-place device in the exchange catheter would interfere with the desired access to that region.
Each of these devices is subject to its own advantages and drawbacks during use. The devices of Shipko et al. and Booker may be somewhat more complex in structure than might be preferred, since it is usually desirable to employ removal devices having a minimal cross-sectional area. The device of Amplatz et al. may require a disadvantageously high degree of axial and/or rotational manipulation before the loop can be slipped over the distal end of the device to be removed. The device of Hyde et al. purportedly avoids this particular problem by having its loop slipped over the proximal end of the in-place device and tightened about it before the exchange catheter is advanced, but not tightened about the in-place device so much that the exchange catheter cannot be readily advanced over the in-place device, or that the in-place device cannot be readily withdrawn. It should go without saying that the device and procedure of Hyde et al. would not be useful for retrieving an elongated structure which have been left in a patient for any extended time, since encapsulation of the structure would prevent any such advancement of the exchange catheter along the structure. Moreover, kinks or surface defects or irregularities in the in-place device could make it difficult or impossible to achieve a desirably precise degree of tightening of the loop about the in-place device. Such surface defects or irregularities could result from minor amounts of encapsulating tissue which remain on the in-place device after severing of the in-place device from the bulk of the encapsulating tissue, or from defects or breakage of the in-place device itself.
It would be highly advantageous to have a snare-type device for removing from a patient a previously implanted elongated structure (such as a catheter, a sheath, a defibrillator lead, a pacemaker lead or the like) which had a minimal cross-sectional profile. It would also be highly advantageous to have such a device which avoided the need for rotational manipulation of the snare, before closure of the snare loop about the elongated structure, to ensure that the snare loop was in fact positioned at a location allowing it to close about the elongated structure. It would further be highly advantageous to have such a device which could be used to remove an elongated structure which had been in place in a patient for a time long enough to become somewhat encapsulated within the body lumen in which the structure was positioned.